The PARAPOPGENE project addressed the application of a novel comparative molecular approach at different evolutionary, ecological and spatial scales to assess the processes acting on microevolutionary scales to generate variability among populations of parasites, to turn later into the processes acting on macroevolutionaly scales to generate species diversity in parasites.

The main objectives were:

1. To explore how population genetic structure and infection levels of parasites with different host’s dispersal abilities were influenced by habitat structure, in particular, the unidirectional river flow.2. To contrast the population genetics and phylogeographic structure of four freshwater trematode species with different life-history strategies and host’s dispersal abilities.3. To validate a DNA-based diagnostic test of identification of larval stages of Diplostomum spp. and develop a rapid method to distinguish between the most frequent Diplostomum species.4. To evaluate the effect of geography and microhabitat preference on the diversity of Diplostomum species.

We used two different host-parasite model systems to address the above objectives during the outgoing (objectives 1and 2) and return (objectives 3 and 4) phase of the project. In rivers, a common process originating from the unidirectional water flow, stream drift, favours the displacement and downstream dispersal of invertebrates. This process could also generate a gradient in infection levels and parasite species genetic diversity, leading to decreasing numbers of parasites per host and decreasing species genetic diversity as one moves upstream from the river mouth. First, to test the effect of unidirectional river current on parasite genetic diversity, we sampled native upland bully fish host (Gobiomorphus breviceps) and collected their trematode species at 10 sites along a 70 km stretch of the Manuherikia River (New Zealand). We analysed the genetic structure of two freshwater trematode species with different life histories (Stegodexamene anguillae and Coitocaecum parvum) using mitochondrial cytochrome c oxidase I gene (cox1) sequences. Second, we tested if the unidirectional water flow, stream drift, could generate a gradient in infection levels, leading to decreasing numbers of parasites per host as one moves upstream from the river mouth. We used four trematode species infecting upland bully fish in the same Manuherikia River settings.